rustc: wrap llvmPackages when using LLVM with callPackage

[RossComputerGuy]

Description of changes

CC @trofi

Use callPackage with pkgsLLVM.rustc.llvmPackages so it fixes eval with Firefox, Betterbird, etc.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[trofi]

How did you test the eval? Maybe I'm doing it wrong. It fails for me as:

$ nix eval github:NixOS/nixpkgs/pull/330754/head#pkgsLLVM.betterbird-unwrapped
error:
       … while calling a functor (an attribute set with a '__functor' attribute)
         at /nix/store/7fzm97kg6m5nh0623wx1b5h45n6g05g0-source/lib/customisation.nix:264:13:
          263|     in if missingArgs == {}
          264|        then makeOverridable f allArgs
             |             ^
          265|        # This needs to be an abort so it can't be caught with `builtins.tryEval`,

       … while evaluating a branch condition
         at /nix/store/7fzm97kg6m5nh0623wx1b5h45n6g05g0-source/lib/customisation.nix:148:7:
          147|     in
          148|       if isAttrs result then
             |       ^
          149|         result // {

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: attribute 'stdenv' missing
       at /nix/store/7fzm97kg6m5nh0623wx1b5h45n6g05g0-source/pkgs/applications/networking/browsers/firefox/common.nix:177:28:
          176|   # LTO requires LLVM bintools including ld.lld and llvm-ar.
          177|   buildStdenv = overrideCC llvmPackages.stdenv (llvmPackages.stdenv.cc.override {
             |                            ^
          178|     bintools = if ltoSupport then buildPackages.rustc.llvmPackages.bintools else stdenv.cc.bintools;

$ nix eval github:NixOS/nixpkgs/pull/330754/merge#pkgsLLVM.betterbird-unwrapped
error:
       … while calling a functor (an attribute set with a '__functor' attribute)
         at /nix/store/7fzm97kg6m5nh0623wx1b5h45n6g05g0-source/lib/customisation.nix:264:13:
          263|     in if missingArgs == {}
          264|        then makeOverridable f allArgs
             |             ^
          265|        # This needs to be an abort so it can't be caught with `builtins.tryEval`,

       … while evaluating a branch condition
         at /nix/store/7fzm97kg6m5nh0623wx1b5h45n6g05g0-source/lib/customisation.nix:148:7:
          147|     in
          148|       if isAttrs result then
             |       ^
          149|         result // {

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: attribute 'stdenv' missing
       at /nix/store/7fzm97kg6m5nh0623wx1b5h45n6g05g0-source/pkgs/applications/networking/browsers/firefox/common.nix:177:28:
          176|   # LTO requires LLVM bintools including ld.lld and llvm-ar.
          177|   buildStdenv = overrideCC llvmPackages.stdenv (llvmPackages.stdenv.cc.override {
             |                            ^
          178|     bintools = if ltoSupport then buildPackages.rustc.llvmPackages.bintools else stdenv.cc.bintools;

Moving formatting changes to a separate commit might get it a bit easier to review what the PR changes WRT evaluation.

[RossComputerGuy]

How did you test the eval?

nix repl. I just looked at my repl history and it seemed I wrongfully assumed the fix worked fully because I am used to the Nixpkgs LLVM WS flake automatically using pkgsLLVM with legacyPackages. I can finish up this fix easily.

[RossComputerGuy]

Ok, it works now.

[trofi]

The pkgsLLVM.betterbird-unwrapped eval succeeds now. Thank you!

[RossComputerGuy]

Only the manual rebuilds on x86_64-linux for some reason but it looks like this is ready and we probably should get it in before #332153, I'll merge if there's no objections.